Add proper JSON output to all API endpoints

[samcorky]

Currently, there are a handful of API endpoints that return a value that is not a JSON array or a JSON object. They return just a string.
/api/version
/api/hostname
/api/wlan/mac

Also, /api/reset doesn't return any response or response code!
I would expect this to return a 202 Accepted HTTP code

[samcorky]

Links to #36

[sjefferson99]

Assuming that is a standard we want to adhere to, this will cause breaking changes, so will need careful testing of the UI and a version bump.

[samcorky]

Happy for discussions